Engineering Tips

If you would prefer to control our USB attenuator or USB RF switch models using Python instead of our standard Windows based GUI test program, JFW does offer a Python library (jfwusb.py). Email our engineering department for the Python library and examples.

Python Library Features:

Auto-discovery of any JFW USB devices connected to the computer.

Set persistent device names for each attenuator.

Set/read attenuator by its device number.

Set/read attenuator by its serial number.

Set/read attenuator by its user defined name.

Set all attenuators to the same dB value, min dB value, or max dB value.

With the push to 5G by wireless cellular providers, lab benches are now being occupied with a greater number of high frequency fixed attenuators with 2.9 mm (aka 2.92 mm) and 2.4 mm RF connectors. It is important to be able to tell these RF connectors apart because 2.4 mm and 2.9 mm connectors will damage each other if mated together. 2.9 mm connectors operate up to 40 GHz. 2.4 mm connectors operate up to 50 GHz. There are notable visible differences between SMA, 2.9 mm and 2.4 mm connectors. SMA and 2.9 mm connectors can be mated to each other without causing damage. Their connector threads are identical and their male/female pin diameters are mechanically compatible. The obvious difference between a SMA female and a 2.9 mm female is the dielectric. SMA female has PTFE dielectric and 2.9 mm has an air dielectric. 2.4 mm connectors are not compatible with SMA or 2.9 mm. The 2.4 mm connectors have a different thread and male/female pin diameters are 56% smaller. The RF specifications for fixed attenuators that work up to 18 GHz, 40 GHz, and 50 GHz vary greatly. The RF specification differences can be seen with these three low power fixed attenuator models: 50HF-xxx SMA (DC-18 GHz), 50HFAR-xxx 2.9mm (DC-40 GHz), 50HFAT-xxx 2.4mm (DC-50 GHz).

The number one FAQ we receive from customers about our remotely controlled test systems is “How easy is it to connect and control the test system?”. So we setup an Ethernet test box that is accessible 24/7 for engineers around the world to try out. It is running our latest 3.x.x firmware. Connect to the test box via a telnet connection at fixed IP address 96.82.36.45 on port 3001. You can use your own telnet program or one of our sample test GUI programs to communicate with the text box. All of our 3.x.x firmware remote commands are detailed with examples in our 3.x.x firmware manual. If you have any firmware or networking questions, you can contact our engineering department directly with questions.

Typical harmonic distortion test setup: Signal Generator, Low Pass Filter, DUT (device under test), Spectrum Analyzer. The low pass filter is used to filter out any high frequency distortion created by the signal generator. The low pass filter ensures that the fundamental test signal (Fc) is the only RF signal being input into the DUT. However, this only cleans up the first half of your harmonic distortion test setup. The other source of distortion that must be accounted for is the harmonic distortion cause by the front end of the spectrum analyzer. Spectrum analyzers cause a substantial amount of signal distortion. It must be accounted for before testing the DUT. Because the distortion caused by the spectrum analyzer is in your testing band you can not use a filter to fix this problem. Instead, use fixed attenuators. Take the DUT out of the test setup. We want to check the harmonic distortion level measured of just our test setup. If you add a 10dB fixed attenuator on the front end of the spectrum analyzer and the difference between Fc and 2Fc increases, then you just improved your test setup. Keep adding 10dB fixed attenuators until the difference between Fc and 2Fc stops increasing. Now your harmonic distortion test setup has been optimized.

The DOCSIS cable TV standard has created the need for equipment verification testing for frequencies up to 1002MHz, 1218MHz, and 1794MHz. JFW offers a number of products for signal routing, signal combining, or signal fading that cover the DOCSIS specified frequencies. JFW Model #75P-193 F is a 75 Ohm solid state programmable attenuator with F female RF connectors. It covers the frequency range 5-2150MHz with an attenuation range of 0-63dB with 1dB steps. The 75P-193 is offered as a component or can be integrated into a remotely controlled (Ethernet/RS-232) attenuator assembly. Please email our engineering department your requirements and we will work with you to find a model for your exact RF testing needs.

Don’t use a fixed attenuator and an adapter, when you can get the fixed attenuator with mixed RF connectors. The majority of fixed attenuators that JFW manufactures can be specified to have mixed RF connectors. They don’t have to be just male/female either. You can specify female/female or male/male. What is the price difference between 50FHC-030-10 SMA Male/Female (standard model) and 50FHC-030-10 SMA Male/N female? No price difference! We stock all of the parts for both models. It takes the same amount of time to build, test, and QC each model. Same price. If you have a specific fixed attenuator requirement, please email our engineering department the details.

Our Drafting Department has created a library of 3D models for almost every JFW model listed on our website. If you would like a 3D model, please email our Drafting Department the 3D model format you prefer (STEP, IGES) and the JFW model number.